Fix MCP null argument binding and culture-dependent history

[Mike Krüger (mkrueger)]

Problem

1. Explicit null arguments failed to bind. MCP clients often send null for optional arguments, for example watch with {"interval": null}. BindMember unwrapped Nullable<T>, and ConvertJsonElement then called GetDouble()/GetInt32()/GetBoolean() on a JSON null, so the call failed with "Invalid value ...".
2. Echoed history used the current culture. FormatOptionForHistory/FormatPositionalsForHistory used ToString(). On de-DE, watch --interval 1.5 was recorded as --interval "1,5", so the recorded command line did not replay correctly.

Changes

• An explicit JSON null for an option or parameter is treated as omitted. It is not bound, not echoed into history, and not counted as a supplied required parameter, so a required parameter passed as null still reports the existing missing-parameter error.
• The paging continuation argument keeps rejecting null, because a null token must not be sent back: it indicates exhaustion unless resultIncomplete is true, which indicates truncated results that cannot be resumed. The rm safety options partition-key (including pk) and etag also reject explicit null before confirmation rather than dropping their safeguards.
• History values are formatted with CultureInfo.InvariantCulture, including array elements.
• docs/mcp.md and the tool schema document null handling, the continuation exception, and incomplete non-resumable results.
• CallTool_EchoCommand_ReturnsSuccessResult now uses a unique message. Other tests record the same echo "hello" "world" line, and history de-duplication made its "history grows by one" assertion depend on test order.

Tests

ToolOperationsCallToolTests covers null for a nullable value-typed option, a string option, and a required parameter, plus invariant history formatting under de-DE. The existing null continuation rejection tests are unchanged.

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation matches the stated behavior and includes appropriate regression coverage and documentation.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes MCP null argument binding and culture-safe command history replay.

Changes:

• Treats explicit null arguments as omitted while preserving continuation-token validation.
• Formats history values using invariant culture.
• Adds focused tests and MCP documentation.

File	Description
docs/​mcp.md	Documents null argument behavior.
ToolOperations.cs	Implements null omission and invariant formatting.
ToolOperationsCallToolTests.cs	Covers null binding, culture formatting, and history isolation.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[github-code-quality]

Code Coverage Overview

Languages: C#

C# / code-coverage/dotnet

The overall line coverage in commit 05a5921 in the dev/mkrueger/fix-mcp... branch remains at 66%, unchanged from commit 6011539 in the main branch.

---

_{Updated October 02, 2026 10:39 UTC}

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation, documentation, and focused regression coverage are consistent and complete.

Review effort: Balanced
Findings: None

[Copilot]

Copilot review overview

🟡 Changes recommended

The new documentation incorrectly treats every null continuation token as exhaustion, overlooking non-resumable truncated results.

Review effort: Balanced
Findings: 1

Open (1)

• Clarify null continuation token when results are incomplete · New

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation, documentation, and focused regression coverage are consistent and complete.

Review effort: Balanced
Findings: None

Resolved since last review (1)

• Clarify null continuation token when results are incomplete